Add connection overlay and Gitea CI/CD workflow

Show full-screen overlay with spinner when server is unreachable,
with periodic health checks that auto-hide on reconnect.
Add Gitea Actions workflow for auto-deploy on release tags.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/css/layout.css

@@ -105,6 +105,48 @@ h2 {
     50% { opacity: 0.5; }
 }
 
+/* Connection lost overlay */
+.connection-overlay {
+    position: fixed;
+    inset: 0;
+    z-index: 10000;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    background: rgba(0, 0, 0, 0.7);
+    backdrop-filter: blur(4px);
+}
+
+.connection-overlay-content {
+    text-align: center;
+    color: #fff;
+}
+
+.connection-overlay-content h2 {
+    margin: 16px 0 8px;
+    font-size: 1.4rem;
+}
+
+.connection-overlay-content p {
+    margin: 0;
+    opacity: 0.7;
+    font-size: 0.95rem;
+}
+
+.connection-spinner-lg {
+    width: 40px;
+    height: 40px;
+    margin: 0 auto;
+    border: 3px solid rgba(255, 255, 255, 0.25);
+    border-top-color: #fff;
+    border-radius: 50%;
+    animation: conn-spin 0.8s linear infinite;
+}
+
+@keyframes conn-spin {
+    to { transform: rotate(360deg); }
+}
+
 /* WLED device health indicator */
 .health-dot {
     display: inline-block;